Boeing was alerted to the alleged drugs ring by members of staff. Managers then called in the FBI, whose agents worked undercover at the plant. It is alleged that those arrested were dealing and buying prescription drugs.

Following a four-year investigation, the US Attorney, Zane David Memeger said 23 people were charged with selling the prescription painkiller Oxycontin and other illegal drugs and 14 were charged with attempted possession of various drugs.

All but one of those charged is a current or former Boeing employee. Another person was expected to be arrested.

“This investigation and prosecution focused not only on the sellers, but also on the users because of the critical role that these employees play in manufacturing military aircraft,” said Memeger.

Boeing employs more than 6,000 people at the Ridley Park plant, where the V-22 Osprey vertical take-off aircraft and H-47 Chinook helicopters are produced.

The Osprey and Chinook are standard US military aircraft used in Iraq and Afghanistan.

Boeing spokesman Damien Mills said the company cooperated with the investigation and made sure the employees under suspicion were in no position to compromise the safety or quality of the aircraft.

The raid found varied amounts of the power painkiller Oxycontin as well as fentanyl, which is sold in lozenge form as Actiq.

It also found the painkiller buprenorphine, which is sold as Suboxone, and the anti-anxiety drug alprazolam, sold as Xanax, said FBI

Boeing issued a statement saying it “commends the US Attorney’s Office and other federal law enforcement agencies for their rigorous and thorough investigation, throughout which we took appropriate steps to ensure safety of our employees and the absolute integrity and quality of the products we produce for our customers”.

If convicted, those charged with distribution face possible sentences of 10 to 260 years in prison and millions of dollars in fines.